1. Field of the Invention
The present invention is directed to a process for increasing the stability of phosphite ligands that are used for homogeneous catalysis and that are susceptible to degradation. In particular, the invention relates to a process wherein an epoxide is added to a catalyst solution containing s phosphite ligand susceptible to such degradation in order to stabilize the ligand against such degradation.
2. Description of Related Art
In many process, a catalyst is used that comprises s phosphite ligand in combination with transition metal. In particular, the Group VIII metals (such as, but not limited to, cobalt, rhodium, and the like) are utilized in such processes. For example, such catalysts are utilized in processes for hydrogenating unsaturated compounds [such as copolymers of s conjugated diene and co-polymerizable monomer(s)] as disclosed in U.S. Pat. Nos. 4,464,515 and 4,503,196; for oligomerizing or dimerizing olefins as disclosed in European Patent Applications 366212 and 177999; for synthesizing optically-active pharmaceuticals as disclosed in U.S. patent application Ser. No. 911,518, filed Jul. 16, 3992; for hydrocyanating butadiene to adiponitrile as disclosed in U.S. Pat. Nos. 4,810,815 and 4,714,773; for decarbonylating aldehydes as disclosed in F. Abu-Hasanayn, M. E. Goldman, A. S. Goldman, J. Am. Chem. Soc. 4 (7), 2520, (1992) and R. B. King, Synlett (10), 671, (1991) and for hydrosilylating olefins as disclosed in U.S. Pat. No. 5,103,033 and in European Application 459464. A particularly important example of such prior art processes is the catalytic hydroformylation of olefinic compounds with carbon monoxide and hydrogen to produce aldehydes.
Thus, British Patent Specification 988,941 discloses the use as a hydroformylation catalyst comprising a Group VIII transition metal-containing and a biphyllic ligand preferably containing trivalent phosphorus. The phosphorus is combined with any organic group. Typically, the disclosed products are alcohols, although aldehyde products also are contemplated. British Patent Specification 1,198,815 discloses carrying out a hydroformylation reaction in the presence of cyclic phosphorus compounds and diphosphines in complexes with cobalt carbonyl.
A rhodium-containing catalyst complex for use in hydroformylation is disclosed in U.S. Pat. No. 3,499,933. The complex is formed with triaryl-phosphite, -arsenite, or -bismuthite. Catalyst for hydroformylation of olefins comprising complexes of iridium or rhodium with biphyllic Group V-A elements, including phosphorous, is disclosed in U.S. Pat. No. 3,644,446. Group VIII transition series metals and poly-phosphite ligands are disclosed for hydroformylation in U.S. Pat. Nos. 4,668,651 and 4,769,498.
Phosphite ligands can be depleted through reaction with components in the hydroformylation reaction mixture. For example, U.S. Pat. No. 4,482,769 postulates the formation of adducts of certain ("open") triorganophosphites with the aldehyde products of the hydroformylation reaction. On the other hand, U.S. Pat. Nos. 4,496,768 and 4,496,749 disclose that certain cyclic phosphite ligands are capable of operating for extended periods of time in hydroformylation reaction mixtures with little or no degradation of the ligand.
U.S. Pat. Nos. 4,599,206 and 4,717,775 disclose a mechanism which causes degradation of ligands used in hydroformylations (i.e., autocatalytic decomposition). In this mechanism, the ligands undergo slow hydrolysis in the presence of water in the reaction mixture. The decomposition products then react with aldehyde product and additional water in the reaction mixture in a series of steps to form hydroxyalkylphosphonic acids. The acids so formed catalyze further hydrolysis of the ligand. Such autocatalytic degradation is a multi-step process which produces diverse phosphorus-containing acids, particularly, phosphorous acids. In the presence of water, these phosphorous acids then catalyze hydrolysis of additional ligand, thus producing additional phosphorous acids. The inevitable "cascade" effect causes hydrolysis of phosphite ligand remaining in the reaction solution to become very rapid and leads to a significant loss of the phosphite ligand.
Such autocatalytic reactions are, in general, well known and are described, for example, in "Kinetics and Mechanisms" by A. A. Frost and R. G. Pearson, John Wiley & Sons Inc., N.Y., 1953, pages 19 and 20. The Figure herein illustrates the increase in concentration of autocatalytic reaction products (e.g., degradation products) with time. Point A in the Figure is the "cascade period", i.e., the period of very rapid, and often virtually uncontrollable, reaction. When the reaction in question is undesirable (e.g., ligand degradation), it is important to maintain the rate of reaction as far below Point A in the Figure as possible, e.g., near Point B.
One method for mitigating degradation of cyclic phosphite ligands used in hydroformylation is disclosed in U.S. Pat. No. 4,567,306. In accordance with this method, a tertiary amine is added to the cyclic ligand that otherwise would degrade by hydrolysis due to ring opening of the cyclic phosphite and the production of acidic materials. The acidic materials catalyze further hydrolysis of the ligand. Tertiary amines reduce ligand destruction by neutralizing the acidic materials and forming ammonium salts. The cyclic ligands used in the method of U.S. Pat. No. 4,567,306 are the ligands disclosed in above-mentioned U.S. Pat. Nos. 4,496,749 and 4,496,768. However, many amines also catalyze the undesirable condensation of the aldehyde products, thus leading to increased formation of undesirable by-products ("heavies") as disclosed by Kosheckima, L. P.; Mel'nichenko, I.V. (Inst. Org. Khim., Kiev, USSR). Ukr. Khim. Zh. (Russ. Ed.), 40(2), 172-4) [Chem. Abstr. 80(23), 132739j, (1974)]. In addition, the above-mentioned U.S. Pat. No. 4,567,306 discloses that the amines do not halt the decay of the "open" ligands disclosed in above-mentioned U.S. Pat. No. 4,496,769.
Ion-exchange methods also have been utilized in an attempt to control acidity and so reduce phosphite ligand degradation. One such method is disclosed in above-mentioned U.S. Pat. Nos. 4,599,206 and 4,712,775. In the method of the latter patents, autocatalytically-produced phosphonic acid by-products are removed from a liquid reaction mixture containing ligand, hydroformylation catalyst and hydroformylation reactants by passing a portion of the mixture over weakly-basic ion exchange resin to remove the undesired acid and the recycling the treated mixture so to the reactor. However, this treatment with ion-exchange resin requires that at least a portion of the catalyst solution be removed from the reactor and treated in an ion-exchange resin bed. Thus, this method requires more catalyst to provide a desired catalyst concentration in the reactor and increases risk of catalyst loss. In addition, a significant additional equipment is required to utilize this method.
The above-described phosphite ligand decomposition products include acidic phosphorous-containing materials. B. Costisella, H. Gross, J. Prakt. Chem., 317(5), 798-806 (1975) ("Costisella Article") discloses the reaction of epoxides and phosphonic acids (alone or in an inert diluent) to produce phosphonate esters by four methods (identified as "Methods A, B, C and D" in the Costisella Article). The epoxides and acids are present in relatively high concentration in the solvent-free reaction mixtures of Methods B and D and in unspecified concentrations in the solvent-containing reaction mixtures of Methods A and C. There is no indication in the Costisella Article of the reaction rate of the epoxide and the acid at low concentrations or of the stability of such ester products against degradation to form acidic by products. It is known from "Physical Chemistry" by P. W. Atkins, W. H. Freeman and Company, San Francisco, Calif., USA, 1978 that reaction rates of non-ionic reactions (such as the reaction disclosed in the Costisella Article) decrease markedly with significant decreases in the concentration of reactants. Hence it would not be obvious from the Costicella Article that low concentrations of epoxides would effectively react with low concentrations of phosphorous acids, particularly in light of the possible competing reaction disclosed in the Lee Article described below.
The above-described hydroformylation processes produce aldehydes. S. B. Lee, T. Takata, T. Endo, Chem. Lett., (11),2019-22, (1990) ["Lee Article"] disclose that, in the presence of catalytic amount of a weak acid, the reaction of epoxides with aldehydes, ketones, lactones, and carbonates produce the corresponding cyclic acetals, orthoesters, and orthocarbonates. The disclosure of the Lee Article suggests that epoxides would react with the aldehyde product in a hydroformylation reaction mixture.
European Pat. No. Application 0 455 261 A1 discloses a process for producing a 1,3-diol (e.g., 1,3-propanediol) and/or a 3-hydroxyaldehyde (e.g., 3-hydroxypropionaldehyde) which comprises contacting an epoxide, carbon monoxide and hydrogen in the presence of a rhodium-containing catalyst composition effective to promote the hydroformylation of the epoxide at conditions effective to form at least one of a 1,3-diol and a 3-hydroxyaldehyde. The rhodium-containing catalyst composition comprises an anionic rhodium-containing complex. Among the rhodium-containing catalysts employed are those having a phosphite ligand. The epoxide may be present in widely varying amounts, for example, in the range of about 0.01% to about 95%, preferably about 0.5% to about 75%, by weight based on the total weight of reactants, catalyst and liquid medium present during this step. In one embodiment, the epoxide hydroformylation occurs in the presence of an electrophile, e.g., H.sup.+ ions, protonic acids, Lewis acids and the like and mixtures thereof, in particular, H.sup.+ ions in an amount effective to further promote the hydroformylation of the epoxide. The molar ratio of acid to rhodium may be in the range of about 0.1 to about 10, preferably about 0.2 to about 10, preferably about 0.2 to about 3. There is no disclosure in this European patent application of the use of an epoxide as an additive (as distinguished from using an epoxide as a principal reactant) or of stabilizing phosphite ligands against degradation by using an epoxide or of the detrimental effects of acids on phosphite ligands.